The present invention relates to a transmission gearbox for bikes, and more particularly, to a transmission gear box whose structure is improved for use in bikes, thus freely shifting transmission modes regardless of the speed of pedals and minimizing a transmission shift shock during shifting the transmission modes.
In general, in the case of existing bikes, a crankshaft distance between a pedal shaft and a pedal is fixed to be constant so that a driveability is determined and provided by only a driving force of pedals combined with the crankshaft.
The driving mechanism that is a structure of determining the driveability for such existing bikes is done within a radius of rotation with a constant rotational torque of the pedal from the pedal shaft. In particular, such a driving mechanism needs more driving energy in upward climbing roads.
In order to improve the above-described conventional defect, it is the most widely generalized to maximize driving energy by providing a transmission gear box to obtain more reasonable driving energy.
However, since the radius of rotation of the pedals that becomes a power source of the driveability is constant, the same driving energy is provided at all times. Accordingly, it is necessary to develop a transmission gear box that can maximize a driveability with a small amount of energy consumption by varying the radius of rotation of the pedals.
To this end, a speed conversion device is mounted in each bike.
An existing speed conversion device for use in bikes, however, has a sequential transmission mode shifting process. Accordingly, the existing speed conversion device for use in bikes has a disadvantage that it is difficult to run unless the transmission gear box is shifted to a low speed transmission mode in the case that each bike stops at a high speed transmission mode and then starts to run again.
In addition, the existing speed conversion device for use in bikes has a drawback that a transmission mode shift shock is caused during shifting transmission modes in a transmission gear box, in particular, the transmission shift shock becomes large during performing a high speed transmission mode shifting process.
In order to solve the above-mentioned problems of conventional art, it is an object of the present invention to provide a transmission gearbox for use in bikes in which structure of the transmission gear box is improved so that a ring gear selected in a gear tooth engagement coupling manner is fixed, to thus manipulate a transmission mode shifting process of a transmission gear unit, and to thereby immediately respond to user's desired transmission ratio regardless of speed of pedals to allow improved responsiveness.